The oil and gas industry is increasingly calling for the development of a new technology that is compact, light weight and most importantly affordable, which can be installed “in-line” and produce a complete set of accurate measurements on each component of multiphase flow.
Various devices are used in the industry, however none is considered capable of meeting satisfactorily all the requirements that are posed by wide ranging set of field conditions in the industry. No single device handles the many flow and fluid conditions that are encountered due to both geological conditions and industrial methods of extraction, and/or meets the precision requirements over the full extent of the large range of flow rates, water cut, and gas fraction that occur in the field. As a result, the devices that exist tend to find niche applications only, or they are combined with other equipments and devices in order to fully service the flow measurements of multiphase fluids. In addition, several devices make use of radioactive sources, which hold significant disadvantages. The use of these sources imposes careful and important containment requirements to mitigate the possibility of contamination, and as a result the industry is reluctant to fully accept methods making use of radioisotopes.
Commercialized MPFMs (multiphase flowmeters) can roughly be divided into two categories:
The first category is based on a pre-requisite step of separation of the liquid and gas phases. Once the liquid and gas phases are separated, the flow measurements are conducted upon the liquid phase and the gas phase separately. The principles of such a method are simple and well known at large and good precision in measurement is generally achieved. This category of MPFM has been widely accepted in the oil industry worldwide. One example is U.S. Pat. No. 6,338,276 B1. The separation of liquid and gas phases are usually achieved using gravity or centrifugal forces. The equipment, called separators, is generally large, difficult to install and relatively costly. The degree of precision/imprecision of the measurements is directly affected by the efficiency of the separation process and compounded by the inherent precision/imprecision of the individual and separate measurements of the liquid and gas phases that are performed after the separation. Room for improvement of the achievable precision inherent to this method is therefore limited. In addition measurements are neither performed in-line or on a real-time.
The second category of MPFMs does not require any fluid pre-separation. It measures directly the various parameters of the multiphase flow. It generally uses an orifice or venturi flowmeter for flow rate measurement. It also uses Gamma radioisotopes, microwaves or capacitance/impedance watercut meters to independently measure watercut and GOR. Generally this method can perform inline real-time measurements of multiphase flow with an acceptable level of precision/imprecision, and it has achieved a degree of acceptance by the industry. An example of this category of device is provided by the Framo Phase Watch VX and U.S. Pat. No. 6,935,189 B2. However, because the method used by such devices is sensitive to interferences in flow regimes and in patterns of multiphase flow, the stability of the measurements represent an issue that is not fully resolved by the technology. In addition, in many areas of the world the water fraction contained in the fluid is disturbed with varying degrees of salinity, affecting the density of the water and the precision of measurements that use impedance/capacitance techniques. The structure of the MPFMs in this category is generally complex and costly. The calibration, installation and maintenance all poses significant operational challenges to the industry.
The main objective of the present invention is to meet the many requirements of the industry with a device that is completely self-sufficient, flow regime independent, compact, light-weight, easy to install and accurate in measuring multiphase flow.